io::Error: avoid double-boxing of custom repr on 32 bits

Author: a1phyr

library/std/src/io/error.rs

@@ -601,7 +601,7 @@ impl Error {
     }
 
     fn _new(kind: ErrorKind, error: Box<dyn error::Error + Send + Sync>) -> Error {
-        Error { repr: Repr::new_custom(Box::new(Custom { kind, error })) }
+        Error { repr: Repr::new_custom(Custom { kind, error }) }
     }
 
     /// Creates a new I/O error from a known kind of error as well as a constant

library/std/src/io/error/repr_bitpacked.rs

@@ -133,8 +133,8 @@ unsafe impl Send for Repr {}
 unsafe impl Sync for Repr {}
 
 impl Repr {
-    pub(super) fn new_custom(b: Box<Custom>) -> Self {
-        let p = Box::into_raw(b).cast::<u8>();
+    pub(super) fn new_custom(b: Custom) -> Self {
+        let p = Box::into_raw(Box::new(b)).cast::<u8>();
         // Should only be possible if an allocator handed out a pointer with
         // wrong alignment.
         debug_assert_eq!(p.addr() & TAG_MASK, 0);
@@ -217,11 +217,11 @@ impl Repr {
     }
 
     #[inline]
-    pub(super) fn into_data(self) -> ErrorData<Box<Custom>> {
+    pub(super) fn into_data(self) -> ErrorData<Custom> {
         let this = core::mem::ManuallyDrop::new(self);
         // Safety: We're a Repr, decode_repr is fine. The `Box::from_raw` is
         // safe because we prevent double-drop using `ManuallyDrop`.
-        unsafe { decode_repr(this.0, |p| Box::from_raw(p)) }
+        unsafe { decode_repr(this.0, |p| *Box::from_raw(p)) }
     }
 }
 

library/std/src/io/error/repr_unpacked.rs

@@ -4,13 +4,13 @@
 
 use super::{Custom, ErrorData, ErrorKind, RawOsError, SimpleMessage};
 
-type Inner = ErrorData<Box<Custom>>;
+type Inner = ErrorData<Custom>;
 
 pub(super) struct Repr(Inner);
 
 impl Repr {
     #[inline]
-    pub(super) fn new_custom(b: Box<Custom>) -> Self {
+    pub(super) fn new_custom(b: Custom) -> Self {
         Self(Inner::Custom(b))
     }
     #[inline]
@@ -26,7 +26,7 @@ impl Repr {
         Self(Inner::SimpleMessage(m))
     }
     #[inline]
-    pub(super) fn into_data(self) -> ErrorData<Box<Custom>> {
+    pub(super) fn into_data(self) -> ErrorData<Custom> {
         self.0
     }
     #[inline]

library/std/src/io/error/tests.rs

@@ -15,10 +15,10 @@ fn test_debug_error() {
     let msg = error_string(code);
     let kind = decode_error_kind(code);
     let err = Error {
-        repr: Repr::new_custom(Box::new(Custom {
+        repr: Repr::new_custom(Custom {
             kind: ErrorKind::InvalidInput,
             error: Box::new(Error { repr: super::Repr::new_os(code) }),
-        })),
+        }),
     };
     let expected = format!(
         "Custom {{ \